Joint for concrete slabs



Oct. 23, 1934- c. J. OBRIEN JOINT FOR CONCRETE SLABS Filed Jan. 19, 19%;: 2 Sheets-Sheet l 00L 23, 1934. Q OBRIEN 1,978,278

JOINT FOR CONCRETE SLABS Filed Jan. 19, 1935 2 Sheets-Sheet 2 Patented Oct. 23, 1934 JOINT'FOR CONCRETE SLABS Chester J. OBrien, Chicago, Ill.

Application January 19,

15 Claims.

My invention relates generally to joints for concrete slabs, but finds its most particular and characteristic expression in joints adapted to control the lines of fracture occurring on the-surface "and internally ofconcrete pavements, and also to. prevent relative, vertical shifting of the slab sections on opposite sides of the joint to thereby maintain the upper surface of the pavement in a substantially smooth or level condition.

After the laying of concrete pavements, the ensuing temperature changes frequently cause the formation of cracks which, unless some means is provided to control them, extendirregularly throughout the pavement and eventually result in the creation of high spots for, after being cracked, the concreteportions on oppositesides of the crack may move relativeto each other in vertical directions. Under these conditions, it is obvious that the pavement, under the impact of heavy vehicular tr'afiic, rapidly deteriorates and, in many cases, becomes positively unsafe for fast moving traffic because of its rough surface. Many attempts have heretofore been made to solve the foregoing problem and the proposed solution has generally taken the form of dividers or so-called crack-locating elementsin the form of sheet metal strips which are embedded vertically in the concrete when the pavement is poured and submerged slightly below the top surface of the slab. These dividers are'intended to reduce the cross-sectional area of the slab along the plane of the dividers so that, if for some reason the tensional stresses in the concrete slab exceed, the strength of the concrete, the divider will cause the pavement to crack along the line of least resistance, that is, a line determined by the divider. As an additional feature, these cracklocating elements are also intended to prevent any relative, vertical shifting of the concrete slab sections after cracking, eitherby providing corrugations in the divider itself, 'or by providing openings through the body thereof through which the concrete flows and across which openings the concrete is expected to, crack within the body of the concrete slab. It is contended that this inter nal crack follows generally a saw-tooth line of more or less irregularconformation and that, be-

1833, Serial No. 652,439

tween the slab sections after cracking occurs, are expensive to make, and, finally, being generally a formed section, are characterized by sharp edges which render them difficult to handle.

It is therefore one of the objects of my invention to devise a crack-locating element or joint member which is adapted to be embedded in a concrete pavement to facilitate surface crackingof the latter along, the line determined by the member, and which is further constructed and arranged to permit a free flowing of the concrete from one side of the member to' the other .during the pouring, this free passage being so arrangedand the member being so constructed that a very definitetongue and groove joint is provided within the interior .of the slab, in the event that cracking occurs, to thereby prevent any relative vertical movements of the slab sections.

A further object is to provide a joint member of the character indicated that is fabricated from rolled steel stripswhich are separated and displaced from each other to form an approximate channel section, the spacing of the strips permitting a free movement of the concrete, from one side of the member to the other when the concrete is poured.

A further object isto provide a joint member composed of three rolled strips, two of which are located in spaced relationin substantially the same'vertical plane'with the third strip displaced laterally from this plane and substantially oppositethe opening between the first two strips, all of the strips being definitely and positivelylocated with respect to each other by means of transversely disposed, tie straps, so that the joint member is characterized by substantially continu ous openings throughout its length which are interrupte'd only by the straps.

A further object is to devise a joint member which, by reason of its fabricated construction, more effectively resists the impact of the concrete when poured thereover, so that no special means is required to maintain its upright position, other than the customary ground locating stakes.

A further object is to provide a joint member composed of a plurality of rolled steel strips which is susceptible 'of adaptation to 'slabs of various thickness merely by changing the length of the tie straps, with a resulting advantage from the standpoint of commercial production, since the same gage and width of strip may be employed for a variety of joint members.

.Afurther object is to devise a joint member 1 in which the openings between the strips can be utilized to receive the ground locating stakes, the substantially continuous nature of these openings enabling the stakes to be driven at any point desired along the length of the member, as often becomes necessary due to the presence of large stones and boulders in the sub-soil.

A further object is to provide a joint member composed of joint sections of a predetermined length, special provision being made at the end of each joint section to receive the adjacent section in such a manner that the adjoining sections are not lapped, but kept strictly in line, so that the surface crack in the concrete slab, should it occur, will be uniform and straight and may be evenly filled with tar and pitch to thereby divide the pavement in regular lanes or squares.

These and further objects of my invention will be set forth in the following specification, reference being had to the accompanying drawings, and the novel means by which said objects are effectuated will be definitely pointed out in the claims.

In the drawings:

Figure 1 is a fragmentary perspective view of my improved joint member, showing part of the same embedded in a concrete slab, with the remaining portion of the member extending therefrom to show the relation of the several component parts.

Fig. 2 is a sectional View through the slab shown in Fig. 1, taken transversely of the joint member, and showing the very definite dove-tailed.

joint provided within the body of the slab in the event that the concrete cracks.

- Fig. 3 is a fragmentary, perspective view showing the adjacent ends of two joint sections prior to their being connected together and clearly showing the manner in which the joint sections are maintained in line, free of any requirement for overlapping the same.

Fig. 4 is a plan View of the improved joint member, as viewed in the direction of the arrow 4 in Fig. 2.

Fig. 5 is a perspective view showing a modified type of strip which is of the expanded metal type, that is, certain portions of the original strip are partially punched or out within the margin thereof to permit the relative displacing or expanding of the cut portions, these displaced portions corresponding to the off-set strip in the joint shown in Fig. 1.

Fig. 6 is a section along the line 6-6 in Fig. 5, looking in the direction of the arrows.

Fig. 7 is a view of the joint member shown in Fig. 5, looking in the direction of the arrow '7 in Fig. 5.

Fig. 8 is a plan view of the joint member shown in Fig. 5 before being expanded, showing the original strip from which thejoint member is made as it appears after being punched or cut.

Fig. 9 is a perspective view of a ground locating stake which may be used in connection with either of the modifications shown.

Fig. 10 is a diagrammatic, sectional view of a modified member, corresponding to Fig. 2, in which the off-set element comprises a simple, flat strip.

Referring to Figs. 1 to 4, inclusive, the numeral T 10 designates my improved joint-forming member which comprises a pair of flat strips 11 and 12, preferably formed from rolled steel and spaced from each other to lie substantially in the same vertical plane. The upper strip 11 is provided along its lower edge with a flange 13 that is bent out of the plane of the strip, while the upper edge of the bottom strip 12 is similarly provided with a flange 14. An intermediate strip 15 is offset from the plane including the strips 11 and 12 and is positioned substantially opposite the opening between the latter strips. The top and bottom edges of the strip 15 are provided with flanges 16 which extend toward and are located substantially in the same plane, respectively, with the flanges 13 and 14.

Intermediate the ends of the member 10, the aforesaid strips are maintained in the relative positions indicated by means of tie bands 17, certain of which may be provided with the aligned apertures 18 for receiving the ground engaging stakes hereinafter described. As clearly shown in Figs. 3 and 4, the several strips, at the left end of the member, are further secured together by means of a relatively narrow band 19 which is riveted, welded, or otherwise secured to the outer surfaces of the strip, whereas the tie bands 17 are preferably secured to the inner surfaces thereof. The opposite, or right end, of the member is defined by a tie band 20 that is somewhat wider than the band 17 and extends beyond the ends of the strips which are secured thereto to provide a plurality of seats 21, against which are placed the adjacent ends of the strips on an associated joint-forming member, so that the'several members will form continuations of each other. The band 20 is further provided with a pair of aligned apertures 22, corresponding to the apertures 18 in the band 1'7, and, when the ends of two mem-- bers, represented by the fragmentary portions shown in Fig. 3, are placed in cooperative relation with the ends of the strips on one member resting against the seats 21 on the band 20, the apertures 22 will be exposed in the openings between the strips on the adjoining member and a ground engaging stake 24 may be driven through these apertures to interlock the ends of the adjoining members and also to maintain the uprightness thereof when the concrete is poured. The stake 24 is preferably in the form of a rolled, T-section. strip 15, apertures 26 may be provided for receiving reinforcing dowels 2'7 that extend transversely of the joint-forming member.

In laying a concrete roadway, or other slab structure, the strip 12 of each member is rested At appropriate intervals along the upon the sub-soil 23 and the stakes 24 are driven through the apertures 18 to maintain the several members in substantially vertical position, those stakes 24 which extend through the apertures 22 additionally serving to hold the ends of adjoining members together. The concrete is then poured over the sub-soil area, including the joint-forming member, and the height of the member is such that the upper edge of the strip 11 is preferably located a short distance below the top surface of the finished slab '28, so that if strains sufiicient to cause cracking are induced in the slab, the top surface thereof will crack substantially along a line 29, which follows generally the upper edge of the strip 11. Moreover, it will be understood that this line of fracture will be substantially straight, owing to the man ner in which the ends of adjoining members are connected together. The manner of resting the ends of one strip against the seats 21 in abutting their regular disposition results in a surfaceof improved appearance, as contrasted with those concrete structures which do not provide for a satisfactory control of the direct-ions in which thesecracks may extend. a

Within the slab, and referring more particu larly to Fig. 2, it will be noted that the disposition of the offset strip 15, relative to the strips 11 and 12, is such as to provide for a free passage of the concrete through the intervening openings from one side of the member to the other, thus avoiding the possibility of any voids or pockets occurring within the slab which is a frequent source of weakness in structures of this type now-in use. In the event of cracking occurring within the slab, the lines of fracture will be substantiallyrestricted to'the planes including the flanges 13 and 16, and 14 and 16, respectively, as denoted generically by the numeral 30 in Fig. 2. Owing to the offset disposition of the strip 15, there will thus be formed within the body of the slab a substantially tongue-and-groove joint, represented by the numeral 31, whose mass and shape is such as to positively resist any tendency of the slab sections on opposite sides of the joint-forming member to move relative to each other in vertical directions, and thus avoiding the creation of any bulges in the roadway surface.

. Owing to its fabricated nature, my improved member is characterized by considerably more stiffness than it is possible to obtain in the sheet metal strips which are now employed in the industry. This feature is extremely important, since it is desirable that the member have sufficient strength to effectively resist the crushing load of the concrete when the latter is poured.

Rolled steel strips are preferred in the making of this member, since they are easier to handle than those formed from sheet metal which are characterized by sharp edges. Rolled strips also enable a substantially constant gageof material to be used, whereas sheet metal members require different thicknesses of material i i-order to meet different specifications for concrete slabs. Strips having a thickness represented by a .No. 14 U. S. standard gage have been found suitable for concrete roadways, although this gage maybe varied as desired. The same strip section may be employed for a variety of roadway requirements, since,for example, having determined the thickness of concrete slab desired, a member of appropriate width may be made simply by choosing tie bands having the correct length. This feature is important from a production standpoint, since it is only necessary to maintain in stock the rolled steel sections noted above and a variety of tie bands having the proper lengths. The use of a single type of strip for a variety of joint forming members also enables the latter to have a weight from 25 to 30 per cent lighter than other members now in use, for any given sage of material, length and width of member.

While the apertures 18 and 22 in the several tie bands are indicated as being the preferred locations for the ground-engaging stakes, it will be apparent that the openings between the strips 15, and-11 and 12, respectively,-provide a plurality of locations for placing the stakes. This versatility in the point of applying the several stakes is of advantage in many instances, since the condition of the subsoil, such as the presence of boulders and stones, frequently prevents the driving ofthe stakes in arbitrary locations. If desired, the flanges on the off-sets'trip .may be eliminated, with a consequent reduction in the cost 'of making themember. The sectional appearance of the member would then be as diagrammatically illustrated in Fig. 10. It has been found that the control of the lines of fracture withinlthe slab do not necessarily require the presence of these flanges, but these flanges may be used to meet certain types of specifications.

In Figs. 5 to 8, inclusive, is illustrated a modified form of my improved member which differs generallyfrom that heretofore described in that it is formed by expanding a metal strip. This new member is represented by the numeral 32 and it is formed from a strip 33 of appropriate length, width and thickness, by first cutting the strip along the longitudinal and transverse lines 34 according to the pattern generally shown in Fig. 8. This severing of the strip 33 provides a plurality of separated elements 35 which may be expanded and oifset from the plane of the strip 33 to assume the positions shown in Figs. 5- and '7. The offset elements 35 correspond generally to the intermediate strip 15 in the modification shown in Fig. 1, while the top and bottom elements 36 and 37 which remain in the strip 33 after the expanding of the element 35, corre-. spond generally to the strips 11 and 12; The expanded elements 35 are integrally united to the elements 36 and 37 by means of the arms 38, while the elements 36 and 37 are integrally connected at the ends of the members by the connecting portions 39.

The manner of using the members shown in Fig. 5 is generally similar to that heretofore described, since the provisionof the expanded elements 35 insures the obtainingof a substantially tongu-and-groove joint within the body of the slab in the event that cracking thereof occurs. The spacing of the elements 35 from the elements 36 and 37 is such as to insure a free passage of the concrete through the intervening openings when the concrete is poured, and these same openings also provide locations for the reception of ground engaging stakes. lhe elements 35 may also be provided with a suitable number of apertures 40 for the reception of the customary dowels that extend transversely of the member.

I claim? 1 A joint-forming member adapted to be embedded in aconcrete slab to act as a crack-locating device, said member having a substantially channel section including openings therethrough through which the concrete may freely pass when poured-to form the slab, the openings being disposed with reference to the section to induce cracking across the planes including the openings to thereby create a substantially llOflglie-and" groove joint between the slab sections on opposite sides of the member. 2. A joint-forming member adapted to be em bedded in a concrete slab comprising elements I spaced from each other, and an offset, intermediate element connected to the first named elements' and separated therefrom by openings through which the concrete may freely pass.

3'. A joint-forming member adapted to be embedded in a concrete slab comprising elements spaced from each other and located substantially in the same plane, and an offset, intermediate element connected to the first named elements and positioned substantially opposite the openingtherebetween, the offset element being separated from the first namedelements by openings through which the concrete may freely pass.

4. A'joint-forming member adapted to be em bedded in a concrete slab comprising fiat strips 71 spaced from each other and located substantially in the same plane, an intermediate strip offset from said plane and located substantially opposite the opening between the first named strips, the intermediate strip being separated from the first named strips by openings through which the concrete may freely pass, and connections between all of said strips for maintaining their relative positions.

5. A joint-forming member adapted to be embedded in a concrete slab comprising a pair of vertically disposed, flat strips spaced from each other and located substantially in the same vertical plane, an intermediate strip offset from said plane and located substantially opposite the opening between the pair of strips, the intermediate strip being separated from the fiat strips by openings through which the concrete may freely pass, and a plurality of tie bands spaced along the length of said strips for connecting the same together and maintaining their relative positions.

6. A joint-forming member adapted to be embedded in a concrete slab comprising a pair of vertically disposed, fiat strips spaced from each other and located substantially in the same vertical plane, an intermediate strip offset from said plane and located substantially opposite the opening between the pair of strips, the intermediate strips being separated from the fiat strips by openings through which the concrete may freely pass, and a plurality of tie bands spaced along the length of said strips for connecting the same together and maintaining their relative positions, certain of said tie bands including aligned apertures for receiving ground-engaging stakes.

7. In combination, a pair of joint-forming members adapted to be embedded in a concrete slab with their upper edges adjacent the top surface of the slab, one member acting as a continuation of the other, each of said members comprising flat, top and bottom strips spaced from each other and located substantially in the same plane, an intermediate strip offset from said plane and separated from the flat strips by openings through which the concrete may freely pass, and means connecting said strips together to maintain their relative positions, said means at the end of one member comprising a tie band having seats to receive the ends of the strips on the other member whereby the strips of both members are substantially aligned with each other.

8. In combination, a pair of joint-forming members adapted to be embedded in a concrete slab with their upper edges adjacent the top surface of the slab, one member acting as a continuation of the other, each of said members comprising flat, top and bottom strips spaced from each other and located substantially in the same vertical plane, an intermediate strip offset from said plane and located substantially opposite the opening between the top and bottom strips, the

intermediate strip being separated from the top and bottom strips by openings through which the concrete may freely pass, and means connecting said strips together to maintain their relative positions, said means at the end of one member comprising a tie band having seats to receive the ends of the strips on the other member whereby the strips of both members are substantially aligned with each other.

9. In combination, a pair of joint-forming members adapted to be embedded in a concrete slab with their upper edges adjacent the top surface of the slab, one member acting as a continuation of the other, each of said members comprising flat, top and bottom strips spaced from each other and located substantially in the same vertical plane, an intermediate strip offset from said plane and located substantially opposite the opening between the top and bottom strips, the intermediate strip being separated from the top and bottom strips by openings through which the concrete may freely pass, and means connecting said strips together to maintain their relative positions, said means at the end of one member comprising an inner tie band having seats to receive the ends of the strips on the other member whereby the strips of both members are substantially aligned with each other, the adjacent ends of the strips on said other member being connected by a narrow, outer tie band which exposes, when said members are operatively associated, a pair of aligned openings in said inner tie band, and a ground-engaging stake extending through said openings to thereby lock said members together.

10. The combination of a concrete slab, and a joint-forming member embedded in the slab with its upper edge adjacent the top surface thereof comprising top and bottom elements spaced from each other, an intermediate element offset therefrom and located substantially opposite the opening between the top and bottom elements, and connections between all of said elements to maintain their relative positions when the concrete is poured, the concrete extending freely through the openings between said elements and said elements being located to induce the concrete to crack in the spaces between the intermediate, and the top and bottom elements, respectively.

11. The combination of a concrete slab, and a joint-forming member embedded in the slab with its upper edge adjacent the top surface thereof and arranged toinduce a crack occurring in the surface of the slab to follow generally the line determined by said upper edge, said member comprising top and bottom elements spaced from each other, an intermediate element offset therefrom and located substantially opposite the opening between the top and bottom elements, and connections between all of said elements to maintain their relative positions, the concrete extending freely through the openings between all of said elements and said intermediate element beill-(l) ing positioned with respect to the top and bottom elements to induce the concrete to crack in the spaces intervening therebetween.

12. The combination of a concrete slab, and a joint-forming member embedded in the body thereof comprising top and bottom strips spaced from each other and arranged substantially in the same vertical plane, the upper edge of the top strip being disposed adjacent the top surface of the slab for inducing such cracks as may occur to follow a line determined by the top strip, an intermediate strip offset from said plane and located substantially opposite the space between the top and bottom strips, said member constituting apermanent part of the slab with the concrete extending freely through the openings between said strips, and means connecting all of said strips for maintaining their relative positions, the intermediate strip being located with respect to the top and bottom strips to induce the concrete slab to crack along the planes including the adjacent edges of the intermediate and the top and bottom strips to thereby produce a substantially tongue-and-groove joint between the sections of the slab on opposite sides of the member.

are

13. The combination of a concrete slab, and a joint-forming member embedded in the body thereof and forming a permanent part of the slab,

said member comprising flat, top and bottom strips spaced from each other and located substantially in the same vertical plane, the upper edge of the top strip being located adjacent the top surface of the slab to induce cracks that may occur in the surface of the slab to follow generally the line determined by the top strip and the facing edges of both strips being flanged outwardly from said plane, a flat, intermediate strip offset from said plane and located substantially opposite the space between the top and bottom strips, the longitudinal edges of the intermediate strip having flanges extending toward the flanges on the top and bottom strips, and connections between all of said strips for maintaining their relative positions, the intermediate strip being located with reference to the top and bottom strips to induce such cracks as may occur within the body of the slab to be located substantially within the planes including the flanged edges of said strips to thereby form a substantially tongueand-groove joint within the slab.

14. A joint-forming member adapted to be embedded in a concrete slab comprising a flat strip expanded within the marginal edges thereof to form an offset, intermediate elementintegrally united with top and bottom elements lying substantially within the plane of the original strip, the intermediate element being separated from the top and bottom elements by openings through which the concrete may freely pass.

15. A joint-forming member adapted to be embedded in a concrete slab comprising a fiat strip expanded in a plurality of locations Within the marginal edges thereof to form a plurality of oifset, intermediate elements, and top and bottom elements lying within the plane of the original strip, all of said members being integrally united together, each of the intermediate elements being separated from its adjacent top and bottom elements by openings through which the concrete may freely pass.

CHESTER J. OBRIEN. 

